This is an investigation of the biological effects on the mammalian retina of prolonged exposure to both coherent and incoherent optical sources. A primary objective is to distinguish between thermal, photochemical and non-linear effects on the retina as influenced by wavelength (1064 nm vs 514.5 nm), spectral bandwidth (380-800 nm, 700- 1400 nm, simulated solar spectrum), retinal irradiance level, exposure time (1, 10, 100, 1000 s and 30 m), irradiated area of the fundus )0.5 micron image diam. on macula vs 2 pi irradiation of entire retina) and time-temperature history. In vivo retinal lesion criteria (funduscopic photography and observation, visual acuity decrement in trained rhesus monkeys) will be related where possible to in vitro assay (histochemistry and electron microscopy). Threshold radiant exposure data will be collected on diabetic retinopathy patients and, where possible, on human volunteers for the purpose of obtaining the limits of variability in man and of testing the validity of existing animal data as related to human data.